[Amir]

Originally Posted by mecamor

hello I wanted to see the shock wave generated by a piston. My problem I can not even move my piston with moving wall. thank you for helping me

Hi,
if you use moving wall, you have just set a boundary condition over that and it wouldn't move. To achieve you purpose, you have to use dynamic mesh instead which as I know, there is special kind for moving piston in cylinder.

Regards,

Amir

[mecamor]

hello
I use moving wall ... but it does not move. I work unsteady. piston speed is 10m / s

[mecamor]

how I should set conditions to limit the piston with moving wall so that the piston moves

[Amir]

Originally Posted by mecamor

how I should set conditions to limit the piston with moving wall so that the piston moves

As I said before, in moving wall method you have just set a boundary condition over that! if you want it to move, use dynamic mesh instead.

[mecamor]

I modeled the cylinder come a rectangle. and also as a piston rectanble. I left a bit of space between the piston and the cylinder. bopundary conditon as I put Moving wall for the piston but still. I'm fluent again. Amir Please do you can give me more detail
thanks you

[mecamor]

Dera amir I put dynamic mesh for the piston or the fluid

[Amir]

Originally Posted by mecamor

Dera amir I put dynamic mesh for the piston or the fluid

The easiest way for you is writing a UDF for the piston and hook to to the piston and with appropriate setting in dynamic mesh panel (smoothing & re-meshing) change the fluid zone cells. it's also better to take a look over manual.

Amir

[mecamor]

Originally Posted by Amir

The easiest way for you is writing a UDF for the piston and hook to to the piston and with appropriate setting in dynamic mesh panel (smoothing & re-meshing) change the fluid zone cells. it's also better to take a look over manual.

Amir

Hi Amir
I wrote the UDF of the piston, but when compiling with C 13 or it Fluent There's an error in line 3. How I should do. thank you
Error: C:\Program Files\ANSYS Inc\v130\fluent\ntbin\win64\PISTON2.c: line 3: parse error.

How I should do. thank you
#include "udf.h"
#include "dynamesh_tools.h"
static real v_prev= 0.0;
DEFINE_CG_MOTION(piston, dt, vel, omega, time, dtime)
{
Thread *t;
face_t f;
real NV_VEC (A);
real force, dv;
/* reset velocities */
NV_S (vel, =, 0.0);
NV_S (omega, =, 0.0);
if (!Data_Valid_P ())
return;
/* get the thread pointer for which this motion is defined */
t = DT_THREAD ((Dynamic_Thread *)dt);
/* compute pressure force on body by looping through all faces */
force = 0.0;
begin_f_loop (f, t)
{
F_AREA (A, f, t);
force += F_P (f, t) * NV_MAG (A);
}
end_f_loop (f, t)
/* compute change in velocity, i.e., dv= F * dt/ mass;
velocity update using explicit eulerformula */
dv= dtime* force / 50.0;
v_prev+= dv;
CX_Message ("time = %f, x_vel= %f, force = %f\n", time, v_prev, force);
/* set x-component of velocity */
vel[0] = v_prev;
}

[Amir]

Originally Posted by mecamor

Hi Amir
I wrote the UDF of the piston, but when compiling with C 13 or it Fluent There's an error in line 3. How I should do. thank you
Error: C:\Program Files\ANSYS Inc\v130\fluent\ntbin\win64\PISTON2.c: line 3: parse error.

How I should do. thank you
#include "udf.h"
#include "dynamesh_tools.h"
static real v_prev= 0.0;
DEFINE_CG_MOTION(piston, dt, vel, omega, time, dtime)
{
Thread *t;
face_t f;
real NV_VEC (A);
real force, dv;
/* reset velocities */
NV_S (vel, =, 0.0);
NV_S (omega, =, 0.0);
if (!Data_Valid_P ())
return;
/* get the thread pointer for which this motion is defined */
t = DT_THREAD ((Dynamic_Thread *)dt);
/* compute pressure force on body by looping through all faces */
force = 0.0;
begin_f_loop (f, t)
{
F_AREA (A, f, t);
force += F_P (f, t) * NV_MAG (A);
}
end_f_loop (f, t)
/* compute change in velocity, i.e., dv= F * dt/ mass;
velocity update using explicit eulerformula */
dv= dtime* force / 50.0;
v_prev+= dv;
CX_Message ("time = %f, x_vel= %f, force = %f\n", time, v_prev, force);
/* set x-component of velocity */
vel[0] = v_prev;
}

Hi,
It doesn't have any error while compiling; try VC++ instead.

[mecamor]

Originally Posted by Amir

Hi,
It doesn't have any error while compiling; try VC++ instead.

Dear amir Whene I compil in fluent I have erro

[AlbertoP]

Hi,

follow this: http://www.cfd-online.com/Wiki/Fluen...with_Fluent_13

You will find how to set Visual C++ to compile UDF, and how to open Fluent depending on the OS you have (32 or 64 bit).

Regards

[samcfd]

Hi everyone,

I want some help regarding an issue i'm facing. I need to write a UDF for rotating an O Grid. To be precise we can rotate using GUI MESH - ROTATE and solve it. But i need to do the same using an UDF. For example i need to rotate the whole domain by 8 deg I give that value in the UDF and the grid gets rotated. Can some1 help me out regarding this.

Thanks in advance,
sam.

[Ahmed Saeed Mansour]

Hello, I wanna write a code to make a variable inlet speed and variable rotating speed (based on the variable velocity) for a rotor in fluent..What should I do?
Thanks

[shri.hade]

Originally Posted by Amir

Hi,
if you use moving wall, you have just set a boundary condition over that and it wouldn't move. To achieve you purpose, you have to use dynamic mesh instead which as I know, there is special kind for moving piston in cylinder.

Regards,

Amir

Hi Amir,
I am working on CFD analysis of a vertical axis wind turbine, in that i need to find RPM of a turbine using fluent.
for this i need to write a UDF but i am totaly unaware of the UDF concept will you please guide me how to write a UDF for this case